Conductor structures can be created based on metallic nanoparticle suspensions printed on plastic or paper substrates and sintered by means of heat and optionally pressure at plastic/paper-compatible temperatures (T<200 C). Such silver nanoinks are readily available from companies such as Cabot or Harima.
The central disadvantages of the conventional thermal treatment include (i) the post-sintering is not area-selective i.e. the entire printed layers are sintered in the oven, (ii) the substrate may emit detrimental gases for the printed structure during thermal treatment of the entire structure and (iii) the durability of the substrate restricts the usable temperature range.
Patent Application FI 20060697, still unpublished when filing the present application, describes an improved method for sintering nanoparticle systems, electrical sintering. In that method, the nanoparticle system conductivity drastically improves under electrical treatment. In comparison with the conventional thermal sintering, the electrical sintering method is fast and reduces the thermal loading of the substrate and other surrounding structures. S. Sivaramakrishnan, et al., Controlled insulator-to-metal transformation in printable polymer composites with nanometal clusters, Nature Materials 6, 149 (2007) and Patent Application publication WO 2007/004033 describe another method for sintering nanoparticles using electric field.
US 2004/0085797 discloses a method for changing the state of nano- or microparticles by means of electric DC voltage. The voltage is applied by electrodes located on surfaces of a flexible, gel-like layer containing dispersed particles, whereby the particles orient aligned to the electric field or form clusters, the conductivity of the structure being locally increased. The method is not well suitable for producing non-volatile structures and cannot be used for forming conductor wires on surfaces.
WO 2005/104226 discloses a method for fabricating through-contacts in semiconductor chips by applying a very high (>1 kV) voltage burst through a nanoparticle-containing layer. The method cannot be used for forming conductor wires on surfaces.
Laser curing [See, e.g., Bieri et al., Superlattices and Microstructures 35,437 (2004)] is also a recognized method for sintering of metal nanoparticle assemblies. However, power transfer to the sintered material is a problem in sintering by optical wavelengths due to high reflectivity of metallic surface. The applicability of laser curing to thicker (t>>10 nm) layers and larger nanoparticles (d>>2 nm) remains questionable.
WO 2007/038950 discloses a method for fabricating metallic patterns on a substrate by coating the substrate with metal particles in the form of said pattern and heating the substrate by microwave radiation. The method does not allow selective patterning of nanoparticle layers.
WO 2005/060008 discloses a method for electrolytic treatment of nanoparticulate layers for the production of solar cells. In the method, a nanoparticulate layer on an electrode can be affected by resistively applying a current through the layer and an electrolytic solution the electrode is immersed in. The method necessitates the use of electrically conductive substrates, can not be carried out at ambient air, for example, and is not suited for selective patterning.